This invention relates to glazing assemblies, in particular to glazing assemblies comprising a laminated panel having at least two sheets of vitreous material between which is a polymeric intervening layer. The invention also relates to processes for the formation of such glazing assemblies.
Certain modem railway vehicles, such as for example the vehicles of high-speed trains, are equipped with glazing assemblies which provide an acoustic isolation effect. The base structure of this assembly is a laminated panel comprising, for example, two sheets of glass having an intervening layer of "acoustic " resin. Thus, in British patent specification GB 2227207-A (Glaverbel), a glazing assembly is described having a laminated panel spaced from a single sheet of clear tempered glass, the panel having an outer sheet of clear tempered glass, an intervening layer of acrylic resin, a second sheet of clear tempered glass and an anti-solar coating.
The intervening layer of acoustic resin provides an attenuation in the acoustic transmission properties of the laminated panel. It is constituted by an adhesive material which secures the sheets of glass. It is a resin which, at ambient temperatures, has high mechanical energy absorption properties and which achieves a less monolithic connection between sheets of glass than the film of polyvinylbutyral usually used as an intervening adhesive for laminated panels, e.g. windshields.
Where there is a need to break through the panel for emergency escape purposes, e.g. when the glazing assembly is used in a vehicle, the panel is subjected to a suitable mechanical force, such as being struck by a hammer, to fracture the panel. The space thus formed may from then on be used as an emergency exit. However, in the case of a laminated panel, after the fracture of the two sheets of glass, the intervening polymeric layer maintains the fragments of glass in place and it is necessary to cut or tear the resin in order to get through the space. This is even more difficult when all the glass sheets of the assembly have been subjected to a thermal tempering treatment. The breaking of thermally tempered glass generates small non-sharp fragments, which are less likely to cause personal injury to persons escaping through the panel.
This operation of cutting the resin is not easy. It may take about 60 seconds to get through an assembly comprising thermally tempered glass and acoustic resin.